A video endoscope includes a generally rigid; elongate insertion member having distal and proximal ends, and a video camera head fixed at the distal end of the insertion member. A sheath fits over and covers the insertion member, the sheath having a distal portion covering the video camera head, at least a section of which distal portion is substantially transparent. The distal portion of the sheath further including a narrowed tip comprising two or more leaves which are closed during insertion through the anus and open apart after insertion to expose the transparent section of the distal portion of the sheath.

The present invention relates generally to medical probes, and specifically to endoscopes.
Various types of endoscopes are known in the art for visual inspection and diagnosis of the rectum and sigmoid of the large intestine. Rigid rectoscopes and sigmoidoscopes are most commonly used for this purpose, since they are durable, easy to use and relatively inexpensive.
To perform an examination using the rigid rectoscope (or sigmoidoscope), the physician first inserts a speculum through the anus. An obturator, having a blunt, rounded distal end, is fitted inside the speculum and protrudes distally therefrom to ease the insertion. Once the speculum is in place, the physician withdraws the obturator and closes the proximal end of the speculum with a plug. A special telescope is fitted into the plug, which enables the physician to view the inside of the rectum and sigmoid at the distal end of the speculum, either by direct vision or using a video camera coupled proximally to the telescope. In order to illuminate the area under view, a light source in an external console is coupled proximally to the speculum by fiberoptics. Typically, the plug also includes one or more working channels, which are used for irrigation, insufflation or insertion of surgical tools through the speculum.
Various rectoscopes and sigmoidoscopes of this type are available commercially. For example, Karl Storz GmbH, of Tuttlingen, Germany, offers the model 24911S rectoscope, which may be used with a rod lens telescope (for example, model 24946B) to view the rectum either under direct view or using a Karl Storz Endovision video camera. The rectoscope and accessories are made from stainless steel to allow disinfection and autoclaving between uses.
Rectoscopes and sigmoidoscopes having a disposable speculum and obturator are also available, such as the KleenSpec disposable sigmoidoscope produced by Welch Allyn Inc., of Skaneateles Falls, N.Y. The speculum and obturator are made of plastic. The speculum clips or screws onto a multi-use handle, to which a light source, telescope, video camera and instruments may be attached.
Flexible sigmoidoscopes and colonoscopes are also known in the art. Most such scopes include a fiberoptic bundle for conveying images from their distal end, within the intestine, to an eyepiece or video camera fixed to the proximal end. Some such scopes, such as the Pentax ES3801 PVE Video Sigmoidoscope, made by Asahi Optical Company of Tokyo, have a CCD detector with an objective lens at its distal end. By comparison with rigid rectoscopes and sigmoidoscopes, however, flexible scopes are costly, fragile and difficult to clean.
It is an object of some aspects of the present invention to provide an improved endoscope, and particularly an improved rectoscope.
It is an object of some aspects of the present invention to provide a video rectoscope that gives improved visibility of anatomical features within the rectum.
It is another object of some aspects of the present invention to provide a rectoscope that is easy and convenient for medical personnel to use.
It is a further object of some aspects of the present invention to provide a rectoscope including an easily-replaceable disposable portion, thus minimizing or eliminating the need for disinfection and sterilization between uses.
It is yet another object of some aspects of the present invention to provide methods and apparatus that facilitate insertion of an endoscope, particularly a rectoscope or sigmoidoscope, into a body cavity.
It is still another object of some aspects of the present invention to provide an improved steering mechanism for an endoscope.
In preferred embodiments of the present invention, a rectoscope comprises an elongate, generally rigid insertion member having a video camera head at its distal end. The insertion member and camera head are covered by a disposable sheath, which includes a transparent distal portion, preferably including an optical window, covering the camera head. The camera head includes an image detector array, preferably a CCD array, as is known in the art, along with a light source for illuminating an area of the intestine viewed by the camera head and an objective lens, which focuses an image of the area onto the array. The sheath, which is preferably made of a biocompatible plastic material, is removed and discarded after use. The rectoscope is used to examine and treat areas of the colon of a patient, specifically the rectal and sigmoid portions of the colon.
By comparison with rigid rectoscopes and sigmoidoscopes known in the art, the present invention can provide substantially improved image quality, because the video camera head is placed at the distal end of the rectoscope, near the area under view. The distal positioning of the camera head enables the present rectoscope to achieve both higher magnification and a wider field of view than video rectoscopes and sigmoidoscopes known in the art, in which the camera head views the intestine through a telescope from the proximal end of the scope.
In preferred embodiments of the present invention, the sheath comprises a narrowed, generally bluntly pointed tip, to ease insertion of the rectoscope through the anus. The narrowed tip thus performs the function of the obturator used in insertion of rectoscopes and sigmoidoscopes known in the art. Elimination of the obturator relieves a physician using the rectoscope of unpleasant odors and possible exposure to infection that are commonly associated with removal of the obturator.
In some preferred embodiments of the present invention, the optical axis of the camera head is angled relative to the longitudinal axis of the insertion member, and the distal end of the sheath is likewise angled, thus defining the narrowed tip. Preferably, the sheath has a bulbous protrusion at the tip, which further eases insertion of the rectoscope through the anus.
In one such preferred embodiment, a mirror is fixed to the bulbous protrusion, which is shaped so that the mirror is positioned within the field of view of the camera head and is oriented obliquely relative to the optical axis thereof An image of the inner wall of the rectum or sigmoid is reflected from the mirror and captured by the camera head. The mirror thus enables the physician to see an image from an alternative view angle, which may be useful particularly in observing and controlling the movement of tools that the physician inserts into the rectum using the rectoscope, as described below.
In other preferred embodiments of the present invention, the narrowed tip of the sheath is formed by a plurality of leaves, formed of a resilient material, which butt together tightly in a closed configuration to cover the transparent portion of the sheath and the camera head. During insertion through the anus, the closed leaves protect the transparent portion from fouling by fecal matter, lubricants or other substances. After the rectoscope has been inserted, the leaves are drawn apart, preferably by pulling the sheath back proximally, so as to expose the transparent portion of the sheath and allow the camera head to receive images of the area of the intestine under view.
In some preferred embodiments of the present invention, the sheath includes one or more worldling channels, which may be used for suction, irrigation, insulation, passage of surgical tools or other functions known in the art. The rectoscope includes a handle, to which the sheath is attached, preferably by a quick connect/disconnect fitting. Preferably, the handle includes user controls for regulating such functions as suction, irrigation and insufflation through the working channels. Further preferably, one or more of the working channels include a one-way valve, to prevent back-flow of fluid (gas or liquid) used in irrigation or insufflation through the channels.
Although rectoscopes in accordance with the present invention are described herein as being generally rigid, in some preferred embodiments the insertion member may include a flexible, resilient longitudinal section. This section allows the rectoscope to bend during insertion into the rectum, to make the insertion easier and less painful for the patient. Such bending is not possible using rigid endoscopes known in the art, and it differs from the bending of flexible endoscopes, which do not have the rigidity to maintain a particular shape and require complex steering mechanisms to control their angle and direction of bend.
In one such preferred embodiment, the rectoscope sheath comprises one or more flexible, longitudinally-disposed inflatable bladders, preferably at least two such bladders disposed radially within the sheath on different sides of the flexible section of the insertion member. Preferably, the bladders are placed on opposing sides of the sheath. The bladders are connected by respective valves to a suitable pressure source. When the pressure in one of the bladders is increased, the bladder lengthens, whereas when the pressure is decreased, the bladder tends to shorten. Thus, the bend angle of the sheath and of the insertion member therein is controlled by varying the pressure in the one or more bladders.
In another preferred embodiment of the present invention, a generally rigid rectal insert having a curved channel therethrough is inserted into the rectum, up to the sigmoid flexure. The insert is turned within the rectum so that the exit from the channel at the sigmoid flexure opens into the intestine in a direction generally along the axis of the sigmoid. The rectoscope including the flexible section, as described hereinabove, is then inserted through the channel and is forced by the rigidity of the insert to bend toward the sigmoid axis. The combination of the insert and rectoscope, in accordance with this preferred embodiment, thus allows endoscopic inspection of a portion of the intestine that can generally be reached only using a more costly flexible endoscope. The rectal insert described herein can also be used in conjunction with flexible endoscopes known in the art, making it easier to pass the endoscope through the sigmoid and reducing pain and the possibility of accidental perforation of the intestine.
Although preferred embodiments are described herein with reference to inspection and treatment of the rectum, and endoscopes in accordance with such preferred embodiments are referred to herein generally as rectoscopes, it will be appreciated that such endoscopes may similarly be adapted and applied to serve as sigmoidoscopes. The principles of the present invention may similarly be applied to produce rigid endoscopes for insertion into other body cavities, such as the throat, the vagina, or any other cavity large enough to receive an endoscope having a video camera head at its distal end, as described herein.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a video endoscope, including:
a generally rigid, elongate insertion member, having distal and proximal ends;
a video camera head fixed at the distal end of the insertion member, and
a sheath, which fits over and covers the insertion member, the sheath having a distal portion covering the video camera head, at least a section of which distal portion is substantially transparent.
Preferably, the camera head includes a detector array and an objective lens, which forms an image on the detector array.
In a preferred embodiment, the camera head is inclined obliquely relative to a longitudinal axis of the insertion member.
Preferably, the camera head includes a light source, most preferably including one or more LEDs.
Preferably, the substantially transparent section of the distal portion of the sheath includes an optical window.
Preferably, the distal portion of the sheath includes a narrowed tip, which facilitates insertion of the endoscope through the anus. Further preferably, the narrowed tip includes a bulbous protrusion.
Alternatively or additionally, the narrowed tip includes two or more leaves, which are closed during insertion through the anus and open apart after insertion to expose the transparent section of the distal portion of the sheath. Preferably, to open the leaves, the sheath is shifted in a proximal direction drawn relative to the insertion member.
Preferably, the sheath contains a worldling channel passing longitudinally therealong. Further preferably, the sheath includes a one-way valve within the worldling channel, for preventing back-flow of fluid therethrough.
Preferably, the endoscope includes a handle, fixed to the proximal end of the insertion member, and the handle includes user controls for controlling the passage of fluid through the working channel.
In a preferred embodiment, at least a longitudinal section of the insertion member is flexible and resilient. Preferably, the sheath includes an inflatable bladder disposed longitudinally within the sheath, such that inflation of the bladder causes its length to increase so that the insertion member bends.
In another preferred embodiment, a mirror is fixed in a position distal to the camera head within a field of view thereof and oriented obliquely relative to an optical axis of the camera head, so that the camera head captures an image reflected from the mirror. Preferably, the image reflected from the mirror includes an area of a physiological structure in which a surgical procedure is to be performed using the endoscope.
There is further provided, in accordance with a preferred embodiment of the present invention, a steering mechanism for an elongate medical probe, including at least one controllably inflatable element fixed to the probe, such that a longitudinal dimension of the element changes responsive to inflation thereof thereby causing the probe to bend.
Preferably, the at least one inflatable element includes two elements disposed radially on different sides of the probe, so as to bend the probe in different, respective directions. Further preferably, the two elements include first and second elements on opposing sides of the probe, such that the first element is inflated and the second element is deflated so as to bend the probe toward the side on which the second element is fixed.
Preferably, the at least one inflatable element includes an expandable wall section on an outer surface thereof, which expands and contracts responsive to changes in the inflation of the element.
Preferably, the mechanism includes a pressure source which is controllably applied to the inflatable element so as control the bending of the probe.
In a preferred embodiment, the probe includes a generally rigid endoscope, having a flexible section which is bent by the mechanism, wherein the endoscope preferably includes a disposable sheath, which includes the at least one inflatable element.
There is moreover provided, in accordance with a preferred embodiment of the present invention, a generally rigid rectal insert, having a distal end which is inserted into the rectum of a patient, the insert having a curved channel therethrough through which an endoscope is inserted into the sigmoid portion of the colon of a patient.
Preferably, the distal end of the insert is brought into proximity with the patient""s sigmoid flexure, and the channel is curved so as to open laterally out of the distal end into the flexure. Further preferably, the insert is rotatable within the rectum so as to align the opening of the channel at the distal end thereof with the intestine.
There is also provided, in accordance with a preferred embodiment of the present invention, a method of endoscopic inspection, including:
providing an elongate, generally rigid insertion member having a video camera head at a distal end of the member;
fitting a disposable sheath over the member, such that the camera head is covered by a substantially transparent portion of the sheath;
inserting the insertion member, covered by the sheath, into a body cavity of a subject; and
receiving video images within the body cavity from the camera head.
Preferably, fitting the sheath includes fitting a sheath having a narrowed tip, and inserting the member includes first inserting the narrowed tip into the cavity.
In a preferred embodiment, the narrowed tip is opened after insertion to expose the substantially transparent portion of the sheath covering the camera head, wherein opening the narrowed tip preferably includes shifting at least a portion of the sheath in a proximal direction over the insertion member so as to separate two or more leaves that meet to form the narrowed tip.
Preferably, receiving the video images includes illuminating the inside of the body cavity using a light source in the video camera head.
Further preferably, fitting the disposable sheath includes fitting a sheath having at least one working channel passing therethrough. In a preferred embodiment, the body cavity is insufflated by passing a pressurized fluid through the working channel.
In a preferred embodiment, providing the insertion member includes providing a member at least a longitudinal portion of which is flexible and resilient, and inserting the member includes flexing the flexible, resilient portion. Preferably, inserting the member includes inserting an insert into the body cavity having a curved channel therethrough, and passing the member through the channel. Alternatively or additionally, flexing the flexible, resilient portion includes inflating an inflatable bladder disposed within the sheath so that the length of the bladder increases, thereby bending the portion.
Preferably, inserting the insertion member includes inserting the member through the anus of the subject, and receiving the images includes receiving images within the rectum or, alternatively or additionally, receiving images within the sigmoid.
There is further provided, in accordance with a preferred embodiment of the present invention, a method for steering a medical probe, including:
fixing an inflatable element to the probe; and
controllably inflating the element so as to change the length thereof, thus causing the probe to bend.
Preferably, fixing the inflatable element includes fixing a plurality of elements on different sides of the probe, so that each element causes the probe to bend in a different, respective direction.
In a preferred embodiment, the medical probe includes a generally rigid endoscope at least a section of which is flexible, and wherein controllably inflating the element causes the flexible section of the endoscope to bend.
There is additionally provided, in accordance with a preferred embodiment of the present invention, a method for inserting an endoscope into the colon of a patient, including:
providing a generally rigid insert having proximal and distal ends and having a curved channel passing therethrough with a lateral opening at the distal end;
inserting the insert into the patient""s rectum so that the distal end is in proximity to the sigmoid flexure of the colon; and
passing the endoscope through the channel and into the sigmoid colon.
Preferably, the insert is rotated to align the opening at the distal end of the insert with the colon before passing the endoscope therethrough.
Preferably, passing the endoscope includes passing a flexible endoscope through the channel or, alternatively, passing a generally rigid endoscope including a flexible portion through the channel, such that the flexible portion is bent by the curve of the channel.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which:


A system and method for programming a digitally tunable oscillator is provided. A desired output frequency is received. A tuning effect of a set of digital tuning words on a crystal resonant frequency is determined, and valid parameters of an algorithm for translating and tuning the crystal resonant frequency to a value within an error tolerance of the desired frequency, based on the determined tuning effect are calculated. Valid parameters are preferably calculated based on an intermediate tuning value, sorted by ascending divide parameter of the algorithm, and then evaluated in sorted order for ability of a tuning effect to null frequency error to within the error tolerance. The valid set of calculated parameters are then programmed into a nonvolatile memory. The oscillator control parameters may remain unprogrammed until all necessary parameters are defined. Because the device may be programmed in a single step, without intermediate presumption of nominal crystal frequency, the final plate process may be unnecessary. A high accuracy may be obtained by searching through the complete set of available parameters for a set that meets a frequency and tolerance specification. The oscillator is preferably a Cypress CY2037 device.

The present invention relates to the field of programmable oscillators, and more particularly to systems and methods for programming high accuracy EPROM programmable phase locked loop oscillators.
The CY2037 from Cypress Semiconductor Corporation, San Jose, Cailf., is an EPROM-programmable (electrically programmable read only memory), high-accuracy, PLL-based (phase-locked loop). The device has low jitter, e.g.,  less than xc2x1100 ps (pkxe2x80x94pk) at 5V and f greater than 33 MHz and  less than xc2x1125 ps (pkxe2x80x94pk) at 3.3V and f greater than 33 MHz. The device is available die form, i.e., without packaging, and attaches directly to a 10-30 MHz crystal. The oscillator device may be packaged into various through-hole or surface mount packages.
Traditionally, the oscillator crystal is calibrated, in an operation termed the xe2x80x9cfinal platexe2x80x9d from within 2,000-3,000 ppm from the nominal frequency desired to within 10-25 ppm typical from the nominal desired frequency. This is a significant mechanical step, which is the final calibration of the oscillator after it is mounted in a module. The final plate involves selectively depositing a film or plating of metal on a prepared pre-plate portion of the surface of the crystal, to mechanically alter the resonant frequency of the crystal. This process is typically manually assisted, requiring a skilled technician to carefully apply the plating to adjust the operating frequency of the crystal. Not only the thickness, but also the placement of the plating is critical; if it is not exactly concentric over the preplate region, phase noise and jitter are increased. In fact, as a rule, phase noise and jitter increase after the final plate. The final plate process also results in loss of yield. For example, there is a probability of plating adhesion failure. Further, the final plate process is performed with the crystal exposed, and thus more sensitive to environmental influences. After the crystal is tuned by the final plate, the crystal is sealed. Thus, the process is expensive, labor consuming, reduces crystal quality, and potentially induces defects.
In principle, the oscillator devices can be stocked as blank parts and custom frequencies programmed in-package at the last stage before shipping from an oscillator manufacturer. This would enable fast-turn manufacture of custom and standard crystal oscillators without the need for dedicated, expensive crystals or inventory of customized assemblies. In this case, the oscillators are not field programmable, and an integrator of oscillators into products must still specifically order a particular oscillator at a predefined frequency, and must still await the customization by the oscillator manufacturer and potential set-up charges, which may be significant for small orders, as well as the added cycle time of days or weeks.
The CY2037 contains an on-chip oscillator and a separate oscillator tuning circuit for fine-tuning of the output frequency. The crystal capacitive load can be selectively adjusted by programming a set of seven EPROM bits. This feature is typically used to compensate for crystal variations or to obtain a more accurate synthesized frequency.
The typical use of a programmable oscillator provides an oscillator crystal trimmed to a nominal value. Then, the oscillator is permanently programmed with the multiply and divide ratios. Finally, at least in the case of the CY2037, the operating frequency of the crystal is tuned with the tuning bits to achieve a desired maximum error.
The CY2037 PLL die has a very high resolution. It has a 12-bit feedback counter multiplier and a 10-bit reference counter divider. This enables the synthesis of highly accurate and stable output clock frequencies with low error, for example zero or low parts per million. The clock can be further modified by eight output divider options of 1, 2, 4, 8, 16, 32, 64 and 128. The divider input can be selected as either the PLL or crystal oscillator output providing a total of sixteen separate output options. The output is selectable between TTL and CMOS duty cycle levels.
The nominal output frequency of the PLL is determined by the following formula:
FPLL=2xc3x97(P+5)/(Q+2)xc3x97FREF
where P is the feedback counter value and Q is the reference counter value. P and Q are EPROM programmable values.
The CY2037 contains a special tuning circuit to fine-tune the output frequency of the device. The tuning circuit consists of an array of eleven logarithmically sized load capacitors on both sides of the oscillator drive inverter. The capacitor load values are EPROM programmable with seven Osc_Tune bits, and can be increased in small increments. As the capacitor load is increased the circuit is fine-tuned to a lower frequency. The capacitor load values vary from 0.17 pF to 8 pF for a 100:1 total control ratio.
The CY2037 uses EPROM programming with a simple 2-wire, 4-pin interface that includes VSS and VDD. Clock outputs can be generated up to 133 MHz at 5V or up to 90 MHz at 3.3V. According to the design, the entire configuration of the EPROM can be reprogrammed one time, allowing programmed inventory to be altered or reused. The CY2037 includes a 44 bit by 2 row EPROM block, which holds all of the configuration information. The programming word contains the data from the EPROM and a row select bit, which determines the row being accessed.
The row select (RowSel) bit of the EPROM word determines the row being read during normal operation. Cypress advises that the bit should match in both rows. Therefore, when row 1 is programmed, row 2 is left unprogrammed, with the RowSel bit row 0=0. When row 1 is programmed, the RowSel bit of row 0 is programmed to 1, a permissible overwrite.
The CY2037 contains EPROM programmable PWR_DWN (Powerdown) and OE (Output Enable) functions. If Powerdown is selected, all active circuitry on the chip is shut down when the control pin goes LOW. The oscillator and PLL circuits must re-lock when the part leaves Powerdown Mode. If Output Enable mode is selected, the output is three-stated and weakly pulled low when the Control pin goes low. In this mode the oscillator and PLL circuits continue to operate, allowing a rapid return to normal operation when the Control input is de-asserted.
In addition, the PWR_DWN and OE modes can be programmed to occur synchronously or asynchronously with respect to the output signal. When the asynchronous setting is used, the powerdown or output three-state occurs immediately (allowing for logic delays) irrespective of position in the clock cycle. However, when the synchronous setting is used, the part waits for a falling edge at the output before powerdown or output enable is initiated, thus preventing output glitches.
The CY2037 contains a shadow register in addition to the EPROM register, which is optionally disabled. The shadow register is an exact copy of the EPROM register and is the default register when the Valid bit is not set. It is useful when the prototype or production environment calls for measuring and adjusting the CLKOUT frequency multiple times. Multiple adjustments can be performed with the shadow register. Once the desired frequency is achieved, the EPROM register is permanently programmed.
Accordingly, the following essential features of the CY2037 are controlled based on data stored in the EPROM:
Feedback counter value (P);
Reference counter value (Q);
Output divider selection;
Oscillator Tuning (load capacitance values);
Duty cycle levels (TTL or CMOS);
Power management mode (OE or PWR_DWN);
Power management timing (synchronous or asynchronous)
Output Source Frequency (PLL or Crystal)
A PLL-based frequency synthesizer uses a reference input to generate output clocks. The reference can be provided by a quartz crystal or an external clock source. The accuracy and stability of the output clocks in a PLL-based frequency synthesizer are directly proportional to those of the reference. Thus, it is important to provide a stable, accurate, and appropriate reference input.
FIG. 1 shows the block diagram of a CY2037 PLL-based frequency synthesizer. The reference input to the PLL comes from an on-chip crystal oscillator. FIG. 2 shows the circuitry of the on-chip crystal oscillator (a.k.a. Pierce oscillator), which is formed by components R, G, Ci and Co, where G is a linear inverter. For this circuit to produce an electrical clock, a quartz crystal needs to be connected between the XTALIN and XTALOUT pins.
The equivalent circuit of a Quartz crystal is shown in FIG. 3. C0 is the shunt or static capacitance of the crystal. R1 is the motional resistance, L1 is the motional inductance, and C1 is the motional capacitance of the crystal. R1, L1 and C1 are determined by the mechanical properties of the crystal (they are in the motional arm of the crystal and their circuit effects only exist when the crystal is oscillating). The effective reactance curve of the crystal is shown in FIG. 4. Thus, it is seen that slight variations in the fabrication of the quartz crystal will alter the nominal output frequency.
When connected as a feedback element in a oscillator circuit that has a 0xc2x0 phase shift, the crystal oscillates at the series resonating frequency (fs) given by Eq. 1:
fs=1/(2xcfx80(L1C1)).xe2x80x83xe2x80x83Eq. 1
A Pierce oscillator has a 180xc2x0 phase shift on the amplifier and needs another 180xc2x0 phase shift from the feedback element. The feedback element in this case is a crystal along with a capacitive load, and the frequency of oscillation of the crystal (and oscillator circuit) is in the xe2x80x9carea of parallel resonancexe2x80x9d. The actual value of the crystal oscillator parallel resonating frequency is dependent on the capacitive loading seen by the crystal and is given by Eq. 2:
fp=fs(1+C1/2(C0+CL)xe2x80x83xe2x80x83Eq. 2
where CL= Capacitive loading seen by the crystal.
For example, a parallel resonant crystal tuned to a particular Cload will oscillate at a predetermined frequency when it is placed in a Pierce oscillator (parallel oscillator) circuit which offers a capacitive loading CL=Cload. If the capacitive loading seen by the crystal in the Pierce oscillator circuit were different from the rated Cload, the change in frequency from the rated frequency is given by Eq. 3:
(fp(rated)xe2x88x92fp(actual))/fp(rated)=C1/2((1/(C0+CL)xe2x88x921/(C0+CL))xe2x80x83xe2x80x83Eq. 3
where:
fp(rated)= frequency rating of crystal
fp(actual)= actual frequency of oscillation in oscillator circuit
Cload= Capacitive loading rating of crystal
CL= Capacitive loading seen by crystal in oscillator circuit.
Thus, the trim capacitor network in the CY2037 would be expected to tune the circuit for variations in the crystal, allowing fine calibration of the operating frequency.
Typically, the selected EPROM register of the CY2037 device is programmed with appropriate multiply (P) and divide (Q) ratios, to achieve a desired output frequency, typically slightly above the desired final frequency. The controller calculates the multiply and divide ratios based on the output of the frequency counter and an algorithm therein, known in the art. After the P and Q are programmed into the device, the output of the oscillator is measured over a number of conditions of tuning, for example testing the effect on the output for each of the tuning bits. The controller then determines an optimal set of tuning bits and these are programmed into the EPROM.
The present invention provides a system and method for field programming an EPROM programmable oscillator device, using a relatively simple programmer device and a terminal or personal computer.
The EPROM programmable oscillator device preferably includes electronically controllable tuning of crystal frequency as well as high precision frequency synthesis. According to the present invention, these two attributes are combined to dispense with the necessity of the final plate, and, for example, to thereby increase output quality (reduced phase noise and jitter), increase product quality (reduce probability of environmental contamination of crystal or delamination of plating), decrease costs, decrease skilled manual labor required, decrease manufacturing cycle time (and allow decentralization of final production steps with field programmability), allow standardization of completely manufactured oscillators, and/or increase manufacturing yield.
Advantages of field programmability include reduced prototype and manufacturing cycle time, and allowing oscillator users to inventory unprogrammed parts, which are programmed to specification as needed.
Oscillators according to the present invention provide programming capability of greater than 6 significant digits of accuracy, over a frequency range of 1 to 125 MHz, covering both the commercial and industrial temperature ranges.
The process essentially determines the free crystal operating frequency, for example over a range of available tuning values, and then calculates the optimal P, Q, divider select and tuning value to achieve the desired oscillator operating frequency with acceptable error (ppm), with the lowest Q value. Therefore, in contrast to typical prior art methods, the crystal tuning is performed simultaneously with selection of oscillator parameters P, Q, and divider select, rather than beforehand. This results in greater flexibility for optimizing the various parameters. In this process, therefore, the P, Q and divider select parameters may vary between oscillators that meet the same output frequency specification, due to differences in the crystal and tuning parameters.
Therefore, one aspect of the invention provides that the system may operate with a grossly tuned oscillator crystal. Another aspect of the invention provides that the oscillator is programmed with both fine-tuning of crystal operating frequency and output frequency translation in a consolidated operation. A further aspect of the invention provides a programming device for a programmable oscillator, which selects optimum crystal frequency tuning and frequency synthesis in a single operation.
Therefore, the present invention provides a human user interface system and method that provides an interface with a programmable oscillator device, for programming thereof, which meet all or some of the objects identified herein.
Initially, the nominal frequency of the crystal is measured using a frequency counter. This frequency is preferably measured with the programmable oscillator in an unprogrammed state, such that the crystal frequency itself is measured Preferably, the tuning sensitivity of the system is also measured, by testing the crystal output over a range of available tuning values. Typically, a small number of measured values are required, for example, eight measurements within a seven-bit tuning system. While the output frequency for each bit combination could also be measured, e.g., all 128 values for a seven bit range, but this is not necessary, as the tuning effects may generally be accurately predicted based on a sparse sampling of this range, preferably testing the sensitivity of each bit, but not necessarily separately. The tuning effects of bits, which represent added capacitance on the crystal, and which lower its operating frequency, are typically non-linear; therefore, a lower order bit will have a reduced effect on output, e.g., result in a lower ppm change, when the total capacitance load on the crystal is higher.
The sensitivity of the tuning bits is tested using a temporary programming technique, e.g., a shadow register. By altering the contents of the shadow register, the capacitive effect of the tuning capacitor loading on the crystal is determined without permanently modifying the oscillator. Thus, the tuning sensitivity may be determined before programming the oscillator, which in the unprogrammed state (e.g., CY2037) outputs the crystal reference without regard for the P, Q and divider select.
After the base frequency and tuning sensitivity of the oscillator are determined, an optimum set of tuning bits, multiply and divide (P and Q) ratios and divider select is determined to minimize ppm error. Since the tuning bits are uncommitted before programming, this provides an additional degree of freedom for selection of the programming conditions of the oscillator as compared with prior designs. In conjunction with high precision P and Q parameters, the method and system according to the present invention achieves higher quality, lower costs, and field programmability. Advantageously, the crystals do not undergo a final plate process, and thus retain low phase noise and jitter.
After the tuning sensitivity is determined, multiply, divide and divider select parameters are calculated, and all are programmed into the device, i.e., in non-volatile memory. Advantageously, a CY2037 device permits programming of the oscillator a second time, in a second register set, allowing device reuse or reallocation, and further minimizing scrap.
The frequency of the oscillator is determined with a frequency counter, which may be internal to the programming device or provided as an external system. Preferably, the system architecture provides a personal computer for interface and control, a frequency counter, for example an IEEE-488 device, and a personality module that performs the direct logical interfacing with the oscillator. However, a single system may be provided, or the functions separated between modules differently. The personality module may be a low cost design, allowing separate dedicated personality modules to be provided for each particular type of oscillator device. The personal computer and frequency counter may be general resources, and need not be dedicated to oscillator programming. It is noted that the personal computer is merely a convenient interface and processing resource, and may be substituted as desired. Using a modern generation personal computer, the entire programming operation is completed in less than 20 seconds per oscillator.
Another embodiment of the invention integrates all required interface and intelligence within the personality module, which in this case is a complete programmer. Likewise, the personality module may include an embedded Web server and communicate with an arbitrary device through a TCP/IP protocol, over any conveniently provided physical transport layer. Because the set of parameters to be analyzed for optimality is large, and the personality module, without having to search the parameter space for the optimum solution, requires little intelligence, it is preferred to employ a separate processor for determining the optimal parameters.
It is also possible to leave the tuning bits unprogrammed, operating the oscillator through the contents of the shadow register. This allows, for example, digital control over the tuning during operation, for example to construct a digital temperature compensated oscillator (TXO). On the other hand, traditional TXO compensation techniques may also be employed, with the device including analog temperature compensation network subjected to the tuning and parameter optimization process. In the case of a digital TXO, a simple thermal sensor interfaces with a simple microcontroller, which then reprograms the tuning bits in the shadow register as necessary to maintain the desired output frequency. Such a digital scheme may also be employed to generate a spread spectrum oscillator output, a fine chirp, or other desired waveforms.
The typical programming algorithm according to the present invention is executed based on the following scheme. An error tolerance is defined, which is the ppm error from a nominal output frequency. The crystal frequency and tuning sensitivity is determined. The algorithm then searches for sets of parameters that translate the measured crystal frequency into the desired frequency, within the error tolerance band. It is generally desirable to employ the lowest divide ratio. The divider select factor provides octave scaling of the frequency over a range of, e.g. seven octaves (CY2037). Therefore, the algorithm searches the parameter space in order of ascending Q for acceptable parameter sets.
In order to achieve low ppm error, phase noise and jitter, it is often desirable to prioritize available parameter sets by Q, ppm error, and divider select, at a mid-tuning range nominal tuning value. The parameter sets are also searched for acceptable sets using tuning values other than the nominal. If necessary, the effect of a proposed tuning value may be tested, to ensure that the results are as expected.
A typical acceptable error tolerance is 150 ppm, which may be available without use of tuning values at all. On the other hand, according to the present invention, the error may typically be held to within xc2x11 ppm. In this case, it is often desirable to activate the four high tuning bits, since this will increase the tuning resolution of the remaining bits. For example, in the CY2037, between the 0000000-0000001 tuning states, the least significant bit has a sensitivity of about 8 ppm; between the 1111110-1111111 states, the least significant bit has a sensitivity of about 2 ppm. Limiting the tuning parameter range will, however, make finding an acceptable set of parameters more difficult.
Thus, with the high level of precision afforded by, for example, the CY2037, it is possible to avoid the xe2x80x9cfinal platexe2x80x9d operation of fabricating an oscillator, using a raw crystal having an error of, for example, up to 2,000 to 3,000 ppm from a nominal desired value. In accordance with the present invention, a program executing on a local host or embedded processor reads a value of the oscillator output and tuning sensitivity, and calculates values of P, Q, and divider select to achieve a desired output frequency range. The tuning algorithm then compensates for residual error, within an error tolerance. For example, such a program is written in Visual Basic(trademark), C, and Access database languages.
This switch capacitor tuning, for potential elimination of the final plate process, takes advantage of the following equation for crystal frequency vs. load capacitance, per equation 2:
xe2x80x83FI=Fr*(C1/(2*C0+CL)+1)xe2x80x83xe2x80x83Eq. 2
This method therefore measures the FI at 8-15 tuning values, for example of a CY2037 device. This implies an approximate value for CI at each tuning value, and then allowing calculation of Fr, C0, C1 and Cstray. This results in the ability to tune the finished oscillator, even with a relatively inaccurate crystal.
The programming interface provides both read and write functions. For reading, the system allows confirmation of the CY2037 and confirmation of the full programming of the CY2037. For writing, the system allows selection of current row, programming of the selected row, and loading of the shadow register with a specified bit pattern.
Where the output is intended to be human readable, the read bit pattern may be annotated, and therefore decoded into portions. In addition, the programming device may act as a translator for multiple oscillator types, and therefore have different personalities. In that case, the annotation feature is, for example, part of a normalization feature for data input and output. Typically, however, the required interface is specific for a certain type of oscillator device, and it is more efficient to provide separate personality modules than a multifunctional programming device.
The programmer preferably interfaces with a standard serial port, e.g., an RS-232 port at 9600 Baud, no parity, 8 data bit and 1 stop bit. Of course, other interfaces could be used, including parallel (Centronics), USB, IEEE-488, Firewire (IEEE-1394), 12C bus, or the like. Further, the programmer may employ an HTML interface and act as an embedded web server, for example including a 10 Base T interface with TCP/IP communications protocol.
Typically, the host system will determine the programming parameters, e.g., P, Q, divider select and tuning bits, and for example, may be fully automated, using a predetermined program to communicate with both frequency counter and programming board.
Alternately, the human user interface may be used to manually enter data into a terminal program, for communication to the programming device. Thus, a separate application may be used to determine appropriate multiply, divide, scaling (divider select) ratios and tuning for the desired output frequency, based on the measured crystal frequency characteristics. The user then transfers these to the programming device through the terminal program.
In the case of an automated testing system, the programming device may be directly controlled by an application program, without use of a manual terminal program interface. In this case, raw, unparsed data may be communicated between the programming device and host computer. However, if the programming device is designed to handle multiple oscillator designs, then a data parser may be of use to standardize communications and the application software in spite of differences in the oscillator integrated circuit design.
The interface for the CY2037 is a four wire interface. The device implements the required Clock/Data In line switch (data/clock), Vpp/Pgm line switch (shift register enable/disable) and Vdd selection (shift/operate), as well as the required programming sequence. The fourth line is a ground.
It is therefore an object of the invention to provide a method for programming a digitally tunable oscillator, comprising the steps of receiving a desired output frequency; determining a tuning effect of a set of digital tuning words on a crystal resonant frequency; calculating valid parameters of an algorithm for translating and tuning the crystal resonant frequency to a value within an error tolerance of the desired frequency, based on the determined tuning effect; and programming in a nonvolatile memory a valid set of calculated parameters.
It is a further object of the invention to provide n apparatus for programming a digitally tunable oscillator, comprising an input for receiving a desired oscillator frequency; an input for receiving an output frequency of the digitally tunable oscillator; a control for selecting a plurality of tuning states of the oscillator; a computer program for calculating valid parameters of an algorithm for translating and tuning the crystal resonant frequency to a value within an error tolerance of the desired frequency, based on received output frequency of the oscillator during the plurality of tuning states; and a programmer for programming a nonvolatile memory of the oscillator with a valid set of calculated parameters.
It is a still further object of the invention to provide a computer readable medium, containing a program for performing the steps of receiving a desired output frequency; determining a tuning effect of a set of digital tuning words on a crystal resonant frequency; calculating valid parameters of an algorithm for translating and tuning the crystal resonant frequency to a value within an error tolerance of the desired frequency, based on the determined tuning effect; and outputting at least one set of calculated valid parameters.
According to various embodiments of the invention, a desired maximum error tolerance is input, constraining the set of valid parameters.
The oscillator is preferably a phase lock loop frequency synthesizer having a multiply parameter and a divide parameter for the frequency translation. The oscillator also preferably has a capacitive load on the crystal, controllable by a tuning word to alter a resonant frequency thereof. According to various embodiments of the invention, substantially all available parameters are evaluated in order to determine the valid parameters. Alternately, a subset of the theoretically available parameters may be evaluated, for example, where bits of the oscillator memory are preprogrammed, or where other considerations are mandated.
It is another object of the invention to provide a system and method for programming a programmable oscillator having a nonvolatile memory for persistently storing a control algorithm and a tuning control, wherein the tuning effect is determined before programming of nonvolatile memory. Therefore, the control algorithm is constrained only by a set of available parameters while determining the tuning control, allowing greater degrees of freedom in calculating the valid parameters.
It is a further object of the invention to provide a separate oscillator programming control and calculating means, and communicating the valid set of parameters between the calculating means and oscillator programming control. Thus, the oscillator programming control need not include a human interface or calculating means, simplifying design and reducing oscillator programming control costs.
It is a still further object of the invention to provide a method and system for programming an accurate oscillator wherein the crystal frequency source is grossly tunes and/or is not subject to a final plate process.
It is another object of the invention to provide a system and method for programming an oscillator having a phase locked loop frequency synthesizer and a crystal tuning parameter, wherein the phase locked loop has a multiply parameter and a divide parameter for frequency synthesis from a crystal frequency, and wherein the valid tuning, multiply and divide parameters are calculated based on an intermediate tuning value, sorted by ascending divide parameter, and then evaluated in sorted order for ability of a tuning effect to null frequency error to within a predefined error tolerance.
These and other objects and features of the present invention will become more fully apparent from the following description and appended claims taken in conjunction with the accompanying drawings, in which like numerals refer to like parts.

System and method for programming oscillators


A printed packaging material and a method for making the same is described. On a primary surface of a thermoplastic flexible packaging material is disposed a printed image. That image includes two primary components. The first is at least one marking containing a pigment. The second is a pigment-free coating which overlies the outermost marking. The coating is made from materials which can polymerize and/or crosslink when exposed to ionizing radiation. After the film is exposed to such radiation, the coating hardens to form a protective layer over the printed markings.

1. Field of the Invention
The present invention relates to the printing of thermoplastic packaging materials, particularly to printing techniques involving the use of radiation curable coatings used to protect underlying layers of printed markings.
2. Background of the Invention
Although printing techniques have become quite specialized and well-defined over the years, the printing of thermoplastic packaging films has remained a bit of a black art. Not until recently have packagers required film manufacturers to provide packaging films bearing photograph quality printed images. This is a significant challenge by itself, but the uses to which some packagers put those films often make a difficult situation even worse.
Packaging applications that require heat shrinkable films present especially challenging problems to film manufacturers. This is due to the need for the printing ink(s) to exhibit sufficient flexibility so as not to crack or flake off once the film has undergone heat shrinking. Those heat shrink applications involving significant amounts of heat, friction, and/or film-to-metal contact magnify the problem all the more. Films intended for cook-in applications can undergo all of these strenuous conditions and provide film manufacturers and converters with some of their greatest printing challenges.
To prevent cracking and/or flaking of printed images, film manufacturers have developed several strategies. Most often, these involve the use of new ink formulations. Standard inks used in the printing of thermoplastic films involve pigments carried in a resin (e.g., nitrocellulose, polyamide, etc.) which is soluble in a carrier solvent (e.g., an alcohol). Once the ink is applied to the film, the solvent evaporates, leaving behind the resin-pigment combination. Newer, more exotic formulations have involved two-part polyurethane resin systems as well as solvent-free systems in which the resin(s) can be cured by means of ultraviolet (UV) light. These new approaches are not without drawbacks, however, due primarily to concerns regarding operator exposure (due to the components causing short term effects such as nausea, headaches, nosebleeds, etc.) and the need to assure that the components have crosslinked to a degree sufficient to ensure that the system complies with applicable governmental food safety regulations. The components used in the two-part system of the former often are not approved for use with food packaging films while the latter requires the presence of photoinitiators which migrate into the packaged product. Both of these are unacceptable to the conscientious film manufacturer.
That which the art has not taught and which remains desirable is a printing technique which allows the use of standard ink formulations but which avoids the cracking and/or flaking problems which those types of ink have exhibited under the strenuous conditions presented by heat shrink applications.
Briefly, the present invention provides a printed thermoplastic flexible packaging material which includes a coating of a material that protects the printed image. The packaging material includes at least two primary surfaces. On at least one of those surfaces, a printed image is applied. The image includes at least one pigment-containing marking derived from a solvent-based ink and a pigment-free coating overlying the outermost pigment-containing marking. The coating includes one or more polymerizable materials, each of which can be cured by ionizing radiation. When the printed packaging material is exposed to ionizing radiation, the coating hardens to form a protective layer over the pigment-containing markings of the printed image.
In another aspect, the present invention provides a method of printing a packaging material. That method involves (a) applying one or more solvent-based inks to a thermoplastic flexible packaging material and allowing or causing the applied ink(s) to become affixed to the packaging material so as to create a pigment-containing marking on the packaging material; (b) applying to the marked packaging material, in a manner which substantially completely covers all of the pigment-containing markings, a pigment-free coating which includes one or more polymerizable materials; and (c) exposing the marked packaging material to ionizing radiation so as to polymerize and, optionally, crosslink the one or more polymerizable materials in the pigment-free coating. Where more than one ink is applied to the packaging material, each ink preferably is applied only after the previous one(s) have become sufficiently affixed to the packaging material that smearing and smudging are avoided.
The method of the present invention provides a distinct and significant advantage over previously described printing methods in that allows for the use of standard solvent-based inks, even where the end use of the printed film involves significant physical and/or chemical abuse. By employing an extremely tough coating over such inks, those inks are protected even through severe handling and processing conditions. This avoids the need for exotic ink systems and/or a tempering of the handling and processing conditions.
The following definitions apply herein throughout unless a contrary intention is expressly indicated:
xe2x80x9ccomprisingxe2x80x9d means including at least, but not limited to, the named materials (in relation to an article or composition), parts (in relation to a machine), or steps (in relation to a method);
xe2x80x9cdisposed on,xe2x80x9d with respect to the location of an ink in relation to the surface layer of the printed film, means coated on or applied to such that it is in intimate contact with a primary surface of the film;
xe2x80x9cflexiblexe2x80x9d means capable of deformation without catastrophic failure;
xe2x80x9cpackagexe2x80x9d means one or more packaging materials (e.g., a film) configured around a product;
xe2x80x9cpolymerxe2x80x9d means the polymerization product of one or more monomers and is inclusive of homopolymers, copolymers, and interpolymers as well as blends and modifications thereof;
xe2x80x9cmer unitxe2x80x9d means that portion of a polymer derived from a single reactant molecule; for example, a mer unit from ethylene has the general formula xe2x80x94CH2CH2xe2x80x94;
xe2x80x9chomopolymerxe2x80x9d means a polymer consisting essentially of a single type of repeating mer unit;
xe2x80x9ccopolymerxe2x80x9d means a polymer that includes mer units derived from two reactants (normally monomers) and is inclusive of random, block, segmented, graft, etc., copolymers;
xe2x80x9cinterpolymerxe2x80x9d means a polymer that includes mer units derived from at least two reactants (normally monomers) and is inclusive of copolymers, terpolymers, tetrapolymers, and the like;
xe2x80x9cpolyolefinxe2x80x9d means a polymer in which some mer units are derived from an olefinic monomer which can be linear, branched, cyclic, aliphatic, aromatic, substituted, or unsubstituted (e.g., olefin homopolymers, interpolymers of two or more olefins, copolymers of an olefin and a non-olefinic comonomer such as a vinyl monomer, and the like);
xe2x80x9c(meth)acrylic acidxe2x80x9d means acrylic acid and/or methacrylic acid;
xe2x80x9c(meth)acrylatexe2x80x9d means an ester of (meth)acrylic acid;
xe2x80x9canhydride-graftedxe2x80x9d means a group containing an anhydride moiety, such as that derived from maleic acid, fumaric acid, etc., has been chemically attached to or affiliated with a given polymer;
xe2x80x9cpermeancexe2x80x9d (in the packaging industry, xe2x80x9cpermeancexe2x80x9d often is referred to as xe2x80x9ctransmission ratexe2x80x9d) means the volume of a gas (e.g., O2) that passes through a given cross section of film (or layer of a film) at a particular temperature and relative humidity when measured according to a standard test such as, for example, ASTM D 1434 or D 3985;
xe2x80x9ccurablexe2x80x9d means capable of polymerization and/or crosslinking;
xe2x80x9cphotoinitiatorxe2x80x9d means a substance which, when exposed to specific wavelengths (e.g., polymerization) or actinic radiation, forms a reactive species that initiates a reaction in one or more other substances in its vicinity;
xe2x80x9csolvent-based inkxe2x80x9d means an ink in which a pigment is dispersed in a polymeric carrier which, in turn, is solvated in a liquid medium such as, for example, water, an alcohol, an ester, or the like;
xe2x80x9ccorona treatmentxe2x80x9d or xe2x80x9ccorona discharge treatmentxe2x80x9d means a process in which one or both primary surfaces of a thermoplastic film are subjected to the ionization product of a gas (e.g., air) in close proximity with the film surface(s) so as to cause oxidation and/or other changes to the film surface(s);
xe2x80x9ccookxe2x80x9d means to heat a food product thereby effecting a change in one or more of the physical or chemical properties thereof (e.g., color, texture, taste, and the like)
xe2x80x9clongitudinal directionxe2x80x9d means that direction along the length of a film, i.e., in the direction of the film as it is formed during extrusion and/or coating;
xe2x80x9ctransverse directionxe2x80x9d means that direction across the film and perpendicular to the machine direction;
xe2x80x9cfree shrinkxe2x80x9d means the percent dimensional change, as measured by ASTM D 2732 (incorporated herein by reference), in a 10 cmxc3x9710 cm specimen of film when subjected to heat;
xe2x80x9cshrink tensionxe2x80x9d means the force per average cross-sectional area developed in a film, in a specified direction and at a specified elevated temperature, as the film attempts to shrink at that temperature while being restrained (measured in accordance with ASTM D 2838, which is incorporated herein by reference);
as a verb, xe2x80x9claminatexe2x80x9d means to affix or adhere (by means of, for example, adhesive bonding, pressure bonding, corona lamination, and the like) two or more separately made film articles to one another so as to form a multilayer structure; as a noun, xe2x80x9claminatexe2x80x9d means a product produced by the affixing or adhering just described;
xe2x80x9cdirectly adhered,xe2x80x9d as applied to film layers, means adhesion of the subject film layer to the object film layer, without a tie layer, adhesive, or other layer therebetween.
xe2x80x9cbetween,xe2x80x9d as applied to film layers, means that the subject layer is disposed in the midst of two object layers, regardless of whether the subject layer is directly adhered to the object layers or whether the subject layer is separated from the object layers by one or more additional layers;
xe2x80x9cinner layerxe2x80x9d or xe2x80x9cinternal layerxe2x80x9d means a layer of a film having each of its principal surfaces directly adhered to one other layer of the film;
xe2x80x9couter layerxe2x80x9d means a layer of a film having less than both of its principal surfaces directly adhered to other layers of the film;
xe2x80x9cinside layerxe2x80x9d means the outer layer of a film in which a product is packaged that is closest, relative to the other layers of the film, to the packaged product;
xe2x80x9coutside layerxe2x80x9d or xe2x80x9csurface layerxe2x80x9d means the outer layer of a film in which a product is packaged that is farthest, relative to the other layers of the film, from the packaged product;
xe2x80x9cbarrier layerxe2x80x9d means a film layer capable of excluding one or more gases (e.g., O2);
xe2x80x9cabuse layerxe2x80x9d means an outer layer and/or an inner layer that resists abrasion, puncture, and other potential causes of reduction of package integrity and/or appearance quality;
xe2x80x9ctie layerxe2x80x9d means an inner layer having the primary purpose of providing interlayer adhesion to adjacent layers that include otherwise non-adhering polymers; and
xe2x80x9cbulk layerxe2x80x9d means any layer which has the purpose of increasing the abuse resistance, toughness, modulus, etc., of a multilayer film and generally comprises polymers that are inexpensive relative to other polymers in the film which provide some specific purpose unrelated to abuse resistance, modulus, etc.
Thermoplastic flexible packaging films find wide use throughout industry and come in a variety of forms and end-use characteristics. Whether the film contains one layer or more than one layer is unimportant as long as the film remains satisfactory for the particular end use application for which it is intended.
Such films often contain at least one layer which includes a polymer including mer units derived from ethylene. Although some ethylene homopolymers are used, interpolymers often are preferred. Exemplary interpolymers include those that include mer units derived from one or more of C3-C20 xcex1-olefins, vinyl acetate, (meth)acrylic acid, and C1-C20 esters of (meth)acrylic acid. lonomers also can be useful. Preferred interpolymers are ethylene/xcex1-olefin copolymers.
The relatively recent advent of single site-type catalysts (e.g., metallocenes) necessitates further definitional clarification when discussing ethylene homo- and copolymers. Heterogeneous polymers are those having relatively wide variation in molecular weight and composition distribution. Polymers prepared with, for example, conventional Ziegler Natta catalysts are heterogeneous. Such polymers can be used in the outside layer of the film, as well as a number of other layers of the film where it has multiple layers.
On the other hand, homogeneous polymers have relatively narrow molecular weight and composition distribution. Homogeneous polymers differ structurally from heterogeneous polymers in that they exhibit a relatively even sequencing of comonomers within a chain, a mirroring of sequence distribution in all chains, and a similarity of chain lengths, i.e., a narrower molecular weight distribution. Homogeneous polymers typically are prepared using metallocene or other single site-type catalysts. Homogeneous polymers also can be used in the printed film of the present invention.
The term xe2x80x9cethylene/xcex1-olefin interpolymerxe2x80x9d as used herein refers both to heterogeneous materials such as low density polyethylene (LDPE), medium density polyethylene (MDPE), linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE), as well as to homogeneous materials which, in general, are prepared by the copolymerization of ethylene and one or more xcex1-olefins. Preferably, the comonomer(s) is/are one or more C4-C20 xcex1-olefins, more preferably one or more C4-C12 xcex1-olefins, and most preferably one or more C4-C8 xcex1-olefins. Particularly referred xcex1-olefins include 1-butene, 1-hexene, 1-octene, and mixtures thereof. In general, from about 80 to 99 weight percent ethylene and from 1 to 20 weight percent xcex1-olefin, preferably from about 85 to 95 weight percent ethylene and from 5 to 15 weight percent xcex1-olefin, are copolymerized in the presence of a single site catalyst. Examples of commercially available homogeneous materials include the metallocene catalyzed Exact(trademark) resins (Exxon Chemical Co.; Baytown, Tex.), substantially linear Affinity(trademark) and Engage(trademark) resins (Dow Chemical Co.; Midland, Mich.), and Tafmer(trademark) linear resins (Mitsui Petrochemical Corp.; Japan).
Homogeneous ethylene/xcex1-olefin interpolymers can be characterized by one or more methods known to those of skill in the art, such as molecular weight distribution (Mw/Mn), composition distribution breadth index (CDBI), narrow melting point range, and single melt point behavior. The molecular weight distribution, also known as polydispersity, can be determined by, for example, gel permeation chromatography. Homogeneous ethylene/xcex1-olefin copolymers to be used in a layer of the film of the present invention preferably have an Mw/Mn of less than 2.7; more preferably from about 1.9 to 2.5; still more preferably, from about 1.9 to 2.3.
The CDBI of homogeneous ethylene/a-olefin interpolymers generally is greater than about 70 percent. CDBI is defined as the weight percent of polymer molecules having a comonomer content within 50% (i.e., xc2x150%) of the median total molar comonomer content. CDBI can be determined by temperature rising elution fractionation as described by, for example, Wild et. al., J. Poly. Sci.xe2x80x94Poly. Phys. Ed., vol. 20, 441 (1982). Linear polyethylene, which does not contain a comonomer, is defined to have a CDBI of 100%. CDBI determination clearly distinguishes homogeneous copolymers (CDBI values generally above 70%) from presently available VLDPEs (CDBI values generally less than 55%).
Homogeneous ethylene/xcex1-olefin interpolymers also typically exhibit an essentially single melting point with a peak melting point (Tm), as determined by differential scanning calorimetry (DSC), of from about 60xc2x0 to 105xc2x0 C., more precisely a DSC peak Tm of from about 80xc2x0 to 100xc2x0 C. As used herein, the phrase xe2x80x9cessentially single melting pointxe2x80x9d means that at least about 80% (by weight) of the material corresponds to a single Tm at a temperature within the range of from about 60xc2x0 C. to 105xc2x0 C., and essentially no substantial fraction of the material has a peak melting point in excess of about 115xc2x0 C. as determined by DSC analysis (e.g., on a Perkin Elmer(trademark) System 7 Thermal Analysis System). The presence of higher melting peaks has been found to be detrimental to film properties such as haze and seal initiation temperature.
Regardless of the type of polymer(s) containing mer units derived from ethylene which is/are used in the outside layer, other layers can be present in the film. For example, the film can include a layer having a low permeance to oxygen, preferably an oxygen permeance at about 23xc2x0 C. and 0% relative humidity of no more than about 150 cm3/m2xc2x7atmxc2x724 hours, more preferably no more than about 100 cm3/m2xc2x7atmxc2x724 hours, even more preferably no more than about 50 cm3/m2xc2x7atmxc2x724 hours, and most preferably no more than about 20 cm3/m2xc2x7atmxc2x724 hours. Such an O2-barrier layer preferably has a thickness of from about 0.001 to about 0.05 mm, more preferably from about 0.002 to about 0.0075 mm, and most preferably from about 0.0025 to about 0.005 mm. Such an O2-barrier layer can include one or more of EVOH, PVDC, polyalkylene carbonate, polyamide, and polyester. Preferably, any O2-barrier layer is an inner layer of a film used according to the present invention.
Where the film includes two or more layers, one or more tie layers can be used to provide increased adherence between the other layers. Such layers often have a relatively high degree of compatibility with polymers used in O2-barrier layers (e.g., EVOH or polyamide) as well as with polymers used in other, non-barrier layers (e.g., polyolefins). When such a tie layer is present, it preferably is disposed on one or both primary sides of the O2-barrier layer, more preferably directly adhered to one or both primary sides of the O2-barrier layer. Such tie layers can include one or more polymers that contain mer units derived from at least one of C2-C12 xcex1-olefin, styrene, amide, ester, and urethane, preferably one or more of anhydride-grafted ethylene/xcex1-olefin interpolymer, anhydride-grafted ethylene/ethylenically unsaturated ester interpolymer, and anhydride-grafted ethylene/ethylenically unsaturated acid interpolymer.
The film also can include one or more other layers which can serve as inner or outer layers and can be classified as bulk layers, abuse layers, etc. Such a layer can include one or more polymers that include mer units derived from at least one of a C2-C12 xcex1-olefin, styrene, amides, esters, and urethanes. Preferred among these are those homo- and interpolymers that include mer units derived from ethylene, propylene, and 1-butene, even more preferably an ethylene interpolymer such as, for example, ethylene/C3-C8 xcex1-olefin interpolymer, ethylene/ethylenically unsaturated ester interpolymer (e.g., ethylene/butyl acrylate copolymer), ethylene/ethylenically unsaturated acid interpolymer (e.g., ethylene/(meth)acrylic acid copolymer), and ethylene/vinyl acetate interpolymer. Preferred ethylene/vinyl acetate interpolymers are those that include from about 2.5 to about 27.5% (by wt.), preferably from about 5 to about 20% (by wt.), even more preferably from about 5 to about 17.5% (by wt.) mer units derived from vinyl acetate. Such a polymer preferably has a melt index of from about 0.3 to about 25, more preferably from about 0.5 to about 15, still more preferably from about 0.7 to about 5, and most preferably from about 1 to about 3.
The film can include a layer derived at least in part from a polyester and/or a polyamide. Examples of suitable polyesters include amorphous (co)polyesters, poly(ethylene/terephthalic acid), and poly(ethylene/naphthalate), although poly(ethylene/terephthalic acid) with at least about 75 mole percent, more preferably at least about 80 mole percent, of its mer units derived from terephthalic acid can be preferred for certain applications. Examples of suitable polyamides include polyamide 6, polyamide 9, polyamide 10, polyamide 11, polyamide 12, polyamide 66, polyamide 610, polyamide 612, polyamide 61, polyamide 6T, polyamide 69, interpolymers made from any of the monomers used to make two or more of the foregoing homopolymers, and blends of any of the foregoing homo- and/or interpolymers.
Preferably, a film used according to the present invention includes from 2 to 20 layers; more preferably, from 2 to 12 layers; more preferably, from 2 to 9 layers; more preferably, from 3 to 8 layers.
Various combinations of layers can be used in the formation of multilayer films. Only 2- through 9-layer embodiments are provided here for illustrative purposes; however, a film according to the present invention can include more layers. Given below are some examples of preferred combinations in which letters are used to represent film layers:
A/B, A/B/A, A/B/C, A/B/D, A/B/C/A, A/B/C/D, A/C/B/C/A, A/B/C/D/A, A/D/B/A, A/B/C/D/Cxe2x80x2, A/B/D/C, A/B/D/C/D, A/C/B/D, A/D/C/D, A/B/D/C/Cxe2x80x2, D/C/D/C/D/C/A, D/C/D/C/A, D/C/A/C/D/B/D/C/A, A/C/D/B/D/C/A
xe2x80x83wherein
A represents a layer that includes a polymer including mer units derived from ethylene (as described supra);
B represents a layer including a polymer having a low permeance to oxygen (as described supra);
C and Cxe2x80x2 represent layers including one or more polymers that include mer units derived from at least one of a C2-C12 xcex1-olefin, styrene, amide, ester, and urethane; and
D represents a layer including a polyester or polyamide.
Of course, one or more tie layers can be used in any of the above structures.
As described previously, the film of the present invention is printed on one of its primary surfaces, preferably on it outside layer. That outside layer preferably includes one or more of a poly(C2-C12 xcex1-olefin), a polyamide, a polyester, poly(vinylidene chloride), and ethylene/vinyl alcohol copolymer.
Regardless of the number and order of layers, one or more conventional packaging film additives can be included therein. Examples of additives that can be incorporated include, but are not limited to, antiblocking agents, antifogging agents, slip agents, colorants, flavorants, antimicrobial agents, meat preservatives, and the like. (The ordinarily skilled artisan is aware of numerous examples of each of the foregoing.) Where the film is to processed at high speeds, inclusion of one or more antiblocking agents in and/or on one or both outer layers of the film structure can be preferred. Examples of useful antiblocking agents for certain applications are corn starch and ceramic microspheres.
A film used according to the present invention preferably exhibits a sufficient Young""s modulus (measured in accordance with ASTM D 882, the teaching of which is incorporated herein by reference) so as to withstand normal handling and use conditions. Typically, a film used according to the present invention exhibits a Young""s modulus in the range of from about 70 to about 1000 MPa. It preferably exhibits a Young""s modulus of at least about 200 MPa, more preferably at least about 300 MPa, and most preferably at least about 400 MPa.
Where a film is intended for end use applications involving heat shrinking, it preferably exhibits a shrink tension in at least one direction of at least about 0.33 MPa, more preferably at least about 0.67 MPa, up to about 3.5 MPa, more preferably up to about 3 MPa. In such instances, the film preferably is heat shrinkable, more preferably biaxially oriented and heat shrinkable. At about 85xc2x0 C., it preferably has a total free shrink of at least about 5%, more preferably at least about 10%, even more preferably at least about 15%.
The measurement of optical properties of plastic films, including the measurement of total transmission, haze, clarity, and gloss, is discussed in detail in Pike, LeRoy, xe2x80x9cOptical Properties of Packaging Materials,xe2x80x9d Journal of Plastic Film and Sheeting, vol. 9, no. 3, pp. 173-80 (July 1993), which is incorporated herein by reference. Specifically, haze is a measurement of the transmitted light scattered more than 2.5xc2x0 from the axis of the incident light. The haze of a particular film is determined by analyzing it in accordance with 1990 Annual Book of ASTM Standards, section 8, vol. 08.01, ASTM D 1003, xe2x80x9cStandard Test Method for Haze and Luminous Transmittance of Transparent Plasticsxe2x80x9d, pp. 358-63, which is incorporated herein by reference. Haze results can be obtained using instrumentation such as, for example, an XL 211 HAZEGARD(trademark) system, (Gardner/Neotec Instrument Division; Silver Spring, Md.), which requires a minimum sample size of about 6.5 cm2. A film used according to the present invention preferably has a haze of less than about 20%, more preferably of less than about 15%, even more preferably less than about 10%, still more preferably less than about 7.5%, and most preferably less than about 5%.
A film used according to the present invention can have any intrinsic gloss value (i.e., gloss prior to printing) as long as the film remains suitable for the intended end use application. Typical gloss values of preferred films for use according to the present invention range from about 25 to about 75%. Gloss can be measured according to the procedure described in ASTM D2457, which is incorporated herein by reference.
Useful films can have any total thickness desired as long as they provide the desired properties, e.g. optics, modulus, seal strength, etc., for a given packaging operation. Nevertheless, films to be used according to the present invention preferably have a total thickness of from about 0.0075 to about 0.25 mm, more preferably from about 0.0125 to about 0.125 mm, even more preferably from about 0.025 to about 0.1 mm, and most preferably from about 0.045 to about 0.075 mm.
Packaging films can be and often are irradiated, which involves subjecting a film material to radiation such as high energy electron treatment. This can alter the surface of the film and/or induce crosslinking between molecules of the polymers contained therein. The use of ionizing radiation for crosslinking polymers present in a film structure is disclosed in U.S. Pat. No. 4,064,296 (Bornstein et al.), the teaching of which is incorporated herein by reference.
If desired or necessary to, for example, increase adhesion to an enclosed meat product, all or a portion of a film can be corona and/or plasma treated. These types of oxidative surface treatment involve bringing a film material into the proximity of an O2- or N2-containing gas (e.g., ambient air) which has been ionized. Exemplary techniques are described in, for example, U.S. Pat. No. 4,120,716 (Bonet) and U.S. Pat. No. 4,879,430 (Hoffman), the disclosures of which are incorporated herein by reference.
Some end use applications can call for films with surface energies of at least about 0.034 J/m2, preferably at least about 0.036 J/m2, more preferably at least about 0.038 J/m2, and most preferably at least about 0.040 J/m2. Regardless of whether an oxidative treatment is used to attain such levels, films having them can be preferred for such end use applications.
A film for use in the present invention can be used to package a variety of products, although it preferably can be used to package a food substance, particularly meat products, cheese, and produce. Examples of meat products that can be packaged include, but are not limited to, poultry (e.g., turkey or chicken breast), bologna, braunschweiger, beef, pork, lamb, and whole muscle products such as roast beef. Examples of produce that can be packaged include, but are not limited to, cut and uncut lettuce, carrots, radish, celery, and the like. The packaging of fluids or flowable materials also is a desirable end use.
A bag can be made from a film by sealing to itself the outer layer, whereby that layer becomes the exterior layer of the bag or by clipping at least one end. The bag can be an end-seal bag, a side-seal bag, an L-seal bag (i.e., sealed across the bottom and along one side with an open top), or a pouch (i.e., sealed on three sides with an open top). Additionally, lap seals can be employed. After forming a bag, a product can be introduced into the bag, and the open end of the bag can be sealed.
Alternatively, a film can be wrapped substantially completely around a product and then heat sealed so as to form a package. Where such a bag or package is made from a heat shrinkable film, the film can shrink around the product when it is subjected to heat. Where the product being packaged is a food product, it can be cooked by subjecting the entire bag or package to an elevated temperature for a time sufficient to effectuate the degree of cooking desired.
Regardless of the structure and end use form of the film to be used, it bears printing on at least its outer surface. Packaging films typically are printed by rotary screen, gravure, or flexographic techniques, with flexography being a preferred method. A preferred flexographic arrangement, involving a central impression cylinder surrounded by print stations, is shown and described in U.S. Pat. No. 5,407,708 (Lovin et al.), the teaching of which is incorporated herein by reference.
The inks used in U.S. Pat. No. 5,407,708 are cured or set by means of radiation. Unlike those inks, however, the inks used in the printed film and printing method of the present invention do not require exposure to radiation. Instead, they can be sufficiently affixed prior to application of subsequent ink layers by means of air and/or heat.
The foregoing inks involve pigment(s) dispersed in one or more standard carrier resins. The pigment can be 4B Toner (PR57), 2B Toner (PR48), Lake Red C (PR53), lithol red (PR49), iron oxide (PR101), Permanent Red R (PR4), Permanent Red 2G (PO5), pyrazolone orange (PO13), diaryl yellows (PY12, 13, 14), monoazo yellows (PY3,5,98), phthalocyanine green (PG7), phthalocyanine Blue, xcex2 form (PB15), ultramarine (PB62), permanent violet (PV23), titanium dioxide (PW6), carbon black (furnace/channel) (PB7), PMTA pink, green, blue, violet (PR81, PG1, PB1, PV3,), copper ferrocyanide dye complexes (PR169, PG45, PB62, PV27), or the like. (Parenthetical identifications in the foregoing refer to the generic color index prepared by the Society of Dyers and Colourists.) Such pigments and combinations thereof can be used to various colors including, but not limited to, white, black, blue, violet, red, green, yellow, cyan, magenta, or orange.
Examples of typical carrier resins used in standard inks include those which have nitrocellulose, amide, urethane, epoxide, acrylate, and/or ester functionalities. Standard carrier resins include one or more of nitrocellulose, polyamide, polyurethane, ethyl cellulose, cellulose acetate propionate, (meth)acrylates, poly(vinyl butyral), poly(vinyl acetate), poly(vinyl chloride), and the like. Typically, such resins are blended, with widely used blends including nitrocellulose/polyamide and nitrocellulose/polyurethane. The latter blend is preferred in the present invention because it can resist penetration of monomers and/or oligomers existing in the overcoat (discussed below).
Ink resin(s) normally are solvated or dispersed in one or more solvents. Typical solvents employed include, but are not limited to, water, alcohols (e.g., ethanol, 1-propanol, isopropanol, etc.), acetates (e.g., n-propyl acetate), aliphatic hydrocarbons, aromatic hydrocarbons (e.g., toluene), and ketones. Such solvents typically are incorporated in amounts sufficient to provide inks having viscosities, as measured on a #2 Zahn cup as known in the art, of at least about 15 seconds, preferably of at least about 20 seconds, more preferably of at least about 25 seconds, and most preferably of from about 25 to about 35 seconds.
Preferably, each of the inks used to make the printed markings on the film surface are essentially free of photoinitiators, thus eliminating the possibility that such materials can migrate toward and into the product to be packaged. Also, the ink(s) preferably are essentially free of waxes, which can prevent uniform distribution and adhesion of the overcoat (discussed below).
Once a first ink layer is applied to the film, the solvent contained therein is allowed to or caused to evaporate. Where a printing system such as that described in the aforementioned patent is employed, the solvent preferably is caused to evaporate by means of heat or forced air so as to reduce the amount of time prior to the next ink layers are applied. Once the first ink layer is applied, all subsequent ink layers (if any) are applied in a similar, standard manner.
Any number of inks can be used to create the printed image. However, cost and space limitations normally impose some practical limit. For printing systems which employ eight print stations, more than one and up to seven different inks preferably are used to apply pigment-containing markings to the film. The use of up to seven inks allows the eighth print station to be reserved for the pigment-free overcoat material, described infra. Alternatively, all eight print stations can be reserved for inks and a pigment-free overcoat material, described infra, applied downstream thereof (preferably on the same printing system). This can allow for complete air drying of the solvents in the inks prior to sealing with the overcoat material.
Once all the various ink layers have been applied to the film surface, a pigment-free overcoat is applied to substantially all of the film surface which has been printed. This overcoat is that which can provide protection to the printed image during further processing, treatment, and use. This overcoat preferably is essentially transparent so that the underlying printed markings are as clearly visible as possible. Preferably, the overcoat material is essentially free of photoinitiators, which eliminates the possibility that such materials can migrate toward and into the product to be packaged.
The overcoat includes one or more polymers or oligomers, optionally mixed with one or more copolymerizable monomers, which polymerize and/or crosslink upon exposure to ionizing radiation. These materials can be monofunctional or have two or more terminal polymerizable ethylenically unsaturated groups per molecule. Energy polymerizable compounds or precursors include, but are not limited to, reactive vinyl monomers, including esters of (meth)acrylic acid, such as beta-carboxyethyl (meth)acrylate; hexanediol di(meth)acrylate; ethoxylated hexanediol di(meth)acrylate; di-, tri-, and/or poly-propylene glycol diacrylate; isobornyl (meth)acrylate; propoxylated glycerol triacrylate; trimethylolpropane tri(meth)acrylate; ethoxylated trimethylolpropane tri(meth)acrylate; propoxylated trimethylolpropane tri(meth)acrylate; polyether diacrylates; bisphenol A diacrylate; aminoplast (meth)acrylates. Other polymerizable compounds include (meth)acrylamides, vinyl acetate, polythiols, and the like. Oligomers include, but are not limited to, (meth)acrylated epoxides, (meth)acrylated polyesters, (meth)acrylated urethanes/polyurethanes, (meth)acrylated polyethers, and (meth)acrylated acrylic oligomers.
Where oligomer(s) are combined with one or more monomers, the viscosity of the mixture preferably is such that it can be printed/applied in a similar matter as solvent-based inks. Typical concentrations of monomer(s) and reactive oligomer(s) and/or polymer(s) can vary from about 5 to about 95% monomer(s) and from about 95 to about 5% reactive oligomer(s) and/or polymer(s). When copolymerizable components are included in the compositions, the amounts used depend on the total amount of ethylenically unsaturated component(s) present; for example, in the case of polythiols, 1 to 98% of the stoichiometric amount (based on the ethylenically unsaturated component(s)) can be used. (These types of materials typically contain small amounts of polymerization inhibitors, processing aids, and other additives. Such additives themselves preferably are reactive so as to become incorporated into the polymer matrix of the overcoat or are of a high enough molecular weight so that the chance of migration into or toward the film is reduced or eliminated. Preferred materials include those that contain (meth)acrylate functionalities, particularly acrylate functionalities.)
The material(s) from which the overcoat is formed can be applied using the same techniques as described previously with respect to the ink(s). Exemplary techniques include, but are not limited to, screen, gravure, and flexographic techniques. Although application of the overcoat can occur separate in time and/or location from application of the ink(s), it preferably occurs in-line with application of the ink(s).
Regardless of the application technique chosen, the thickness of the resulting overcoat preferably is sufficient to provide good scratch resistance (during film handling and processing) and chemical resistance to, e.g., fatty acids, oils, processing aids, etc., but not so thick as to prevent the overcoat from shrinking or flexing with the film as required by the application(s) to which the film will be put. Generally, useful overcoat thicknesses can range from about 0.5 to about 12 xcexcm, preferably from about 1 to about 10 xcexcm, more preferably from about 1.5 to about 8 xcexcm, and most preferably from about 2 to about 5 xcexcm.
Once the overcoat is applied, the printed film is exposed to ionizing radiation. This polymerizes and/or crosslinks the materials in the overcoat, thus providing a hardened xe2x80x9cshellxe2x80x9d over the underlying printed markings. Useful types of ionizing radiation include electron beam (e-beam), X-ray, corona discharge, and the like, with the former being preferred. Regardless of source, the dose of ionizing radiation preferably is sufficiently high to polymerize and crosslink the overcoat sufficiently yet not so high so as to degrade the underlying printed markings or the surface of the film. Generally, useful radiation dosages can range from about 50 to about 250 keV, preferably from about 55 to about 200 keV, and more preferably from about 60 to about 150 keV. (Conventional e-beam irradiation units operate at higher voltages and are believed to produce electrons which pass through the coating without effectively and efficiently curing the total coating. Although not scientifically proven at this time, new low voltage (60-100 keV) e-beam irradiation units such as those commercially available from Applied Advanced Technologies (Winchester, Mass.) are believed to incorporate one or more materials in the window of the unit that allow electrons to pass therethrough at a lower velocity and render a more effective cure to the overcoat surface.)
If the processing techniques employed allow for the use of a low oxygen environment, the coating and irradiation steps preferably occur in such an atmosphere. A standard nitrogen flush can be used to achieve such an atmosphere. The oxygen content of the coating environment preferably is no greater than about 300 ppm, more preferably no greater than about 200 ppm, even more preferably no greater than about 100 ppm, still more preferably no greater than about 50 ppm, and most preferably no greater than about 25 ppm with a completely oxygen-free environment being the ideal.
Regardless of the intrinsic gloss of the film used, the printed film preferably exhibits a gloss of at least about 50%, more preferably at least about 65%, and more preferably at least about 75% subsequent to application and irradiation of the overcoat. Additionally, the gloss level of the overcoat itself preferably is at least about 75%.
The above-described techniques can be used with a variety of packaging materials, including those used for the packaging of beef, pork, poultry, cheese, produce, liquids, pet foods, and the like. A preferred application involves those packaging materials used in conjunction with food products that are processed in thermoplastic film packages by subjecting the packaged product to elevated temperatures (e.g., hot water or steam), i.e., cook-in. Various meat products, such as pork, sausage, poultry, mortadella, bologna, beef, braunschweiger, etc., are prepared as cook-in products; certain non-meat proteinaceous products such as soybean can be processed similarly. In all these cases, obtaining adequate film-to-food adhesion and providing a snug package can be necessary for acceptable aesthetic appearance.
Packaging materials for use in cook-in applications typically are produced in roll form and then, after printing, converted into shirred sticks, bags, pouches, and the like for the end user. Accordingly, a cook-in film must be capable of withstanding exposure to solvents (e.g., mineral oil), mechanical stresses (e.g., bending), high temperatures, high pressure, abrasions, etc., for extended periods of time while not compromising its ability to contain the food product or its flexibility. During a typcial conversion process, about 75 m of film is mechanically compressed into about 0.75 m. Often the process speed, pressure, and mineral oil causes adhesive failure of standard ink systems to the underlying film.
In cook-in applications, the packaging material typically is segmented and filled with a meat product slurry. The package is forced into a stainless steel mold and submerged in a cook tank, normally for a fairly lengthy cook cycle. Submersion in hot (i.e., about 55xc2x0 to 65xc2x0 C.) water for up to about 4 hours is common; submersion in 70xc2x0 to 100xc2x0 C. water or exposure to steam for up to 12 hours is not uncommon, although most cook-in procedures normally do not involve temperatures in excess of about 90xc2x0 C. Following the cook-in process, the film or package preferably conforms, if not completely then at least substantially, to the shape of the contained food product.
The printed film of the present invention retains at least about 80%, preferably at least about 85%, more preferably at least about 90%, of its printed markings even after being subjected to elevated temperatures such as, for example, 70xc2x0 C. for extended periods of time such as, for example, an hour or more.
Objects and advantages of this invention are further illustrated by the following examples. The particular materials and amounts thereof, as well as other conditions and details, recited in these examples should not be used to unduly limit this invention.

Method of providing a printed thermoplastic film having a radiation-cured overprint coating